1. Field of the Invention
The present invention relates to a digital video camera and, more particularly, to an apparatus suitably used in a video camera apparatus for converting an analog video signal obtained by an image pickup element into a digital video signal and performing digital signal processing.
2. Related Background Art
FIGS. 1A and 1B show a conventional video camera apparatus for A/D-converting an analog signal output from a solid-state image pickup element, and performing signal processing in a digital form. Referring to FIGS. 1A and 1B, a video signal obtained via a lens element 1, a solid-state image pickup device 2, a correlation double sampling circuit 3, and a gain adjustment circuit 4 is sampled by an A/D converter 5 to be converted into a digital signal.
The sampled digital signal is supplied to a digital signal processing circuit 6. The digital signal processing circuit 6 generates a digital luminance signal and digital color-difference signals from the input digital signal. The digital luminance signal generated by the digital signal processing circuit 6 is converted into a band-limited analog luminance signal via a D/A converter 12 and a low-pass filter 13.
The digital color-difference signals are converted into band-limited analog color-difference signals via D/A converters 35 and 36 and low-pass filters 37 and 38. Furthermore, the analog color-difference signals are supplied to a modulation circuit 39 to be converted into an analog chrominance signal. The analog chrominance signal is supplied to a digital signal recording device 21 together with the analog luminance signal. The processing so far is executed at the sampling frequency of the image pickup element.
When YC-separated input signals are externally input as a video signal, these signals are respectively input to switch circuits 8 and 9. When a composite video signal VIDEO is input, the signal VIDEO is separated into luminance and chrominance signals by a luminance/chrominance separation circuit 7, and the separated signals are input to the switch circuits 8 and 9. One of these YC-separated input signals and the composite video signal is selected by the switch circuits 8 and 9.
The analog luminance and color-difference signals from a camera and externally input analog luminance and color-difference signals are selected by switch circuits 14 and 15. The frequency band of the analog luminance signal is limited by a low-pass filter 17. The band-limited analog luminance signal is supplied to an A/D converter 18 to be converted into a digital luminance signal.
The analog chrominance signal is converted into analog color-difference signals by a demodulation device 40, and the analog color-difference signals are then converted into digital color-difference signals by A/D converters 41 and 42. In this case, the A/D conversion is performed at the sampling frequency of a digital VTR.
The digital signal recording device records the digital luminance and color-difference signals, which are converted, as described above, on a magnetic tape 22. Thus, a digital video signal is recorded.
At this time, switch circuits 25 and 26 are switched to the REC side, and the analog luminance and chrominance signals are selected and output by the switch circuits 25 and 26. An EVF 33 performs a display operation based on the output luminance and chrominance signals for monitoring an image pickup operation.
In a reproduction mode, the digital signal recording device 21 generates digital reproduced luminance and color-difference signals from a signal reproduced from the magnetic tape 22. Of these signals, the reproduced luminance signal is converted into an analog luminance signal by a D/A converter 23 which operates at the sampling frequency of the digital VTR, and thereafter, the frequency band of the analog luminance signal is limited by a low-pass filter 24, thus obtaining an analog reproduced luminance signal.
On the other hand, the digital color-difference signals are converted into analog color-difference signals by D/A converters 28 and 29 which operate at the sampling frequency of the digital VTR. The frequency bands of these analog color-difference signals are then limited by low-pass filters 30 and 31 to obtain an analog reproduced color-difference signal. Furthermore, the analog reproduced color-difference signal is modulated by a modulation device 32.
At this time, the switch circuits 25 and 26 are switched to the PB side, selecting the modulated analog reproduced color-difference signals together with the analog reproduced luminance signal, and output these signals as a reproduced video signal.
In the case of the conventional digital video camera apparatus shown in FIGS. 1A and 1B, in order to allow recording/reproduction of both digital luminance and color-difference signals from the camera and external analog luminance and color-difference signals, many A/D converters, D/A converters, and the like are required. For this reason, the circuit scale constituting the digital video camera apparatus becomes large, and it is difficult to reduce cost.
In conventional image pickup recording apparatuses adopting a digital signal processing system, an image pickup signal processing circuit is an analog circuit, and an output signal from the analog processing circuit is converted into a digital signal. For this reason, due to a large circuit scale, the number of components becomes large, and current consumption undesirably increases. Also, it is difficult to make the apparatus compact, and to reduce cost.
Since the apparatus includes both an analog signal processing circuit and a digital signal processing circuit, a sufficient S/N ratio cannot often be obtained due to interference such as mixing of a digital signal into an analog signal, and the apparatus cannot be rendered compact.
Since the image pickup signal processing circuit adopts analog processing, image quality is determined by performance such as the frequency characteristics, noise characteristics, a change in performance due to a change in temperature, a variation in characteristics in units of circuits, and the like, and it is difficult to achieve high image quality.
In order to attain special effects using a frame memory and a digital calculation, a still larger number of circuit components are required. As a result, it is difficult to make the apparatus compact, and power consumption undesirably increases.
The present invention has been made in consideration of the above-mentioned problems, and has as its object to simplify the circuit arrangement of a digital video camera apparatus which selects one of a video signal from a digital video camera and a video signal from an external input terminal, and records the selected video signal on a recording medium.
The present invention has been made to solve the above-mentioned problems, and has as its another object to provide a digital video camera apparatus having a small number of components.
The present invention has been made in consideration of the above-mentioned problems, and has as its still another object to simplify the circuit arrangement of an apparatus for digitally recording an image pickup signal.
In a digital video camera apparatus according to an aspect of the present invention, which comprises a digital signal processing circuit and a digital signal recording device and in which an analog video signal supplied from an image pickup element is converted into a digital video signal, the converted digital video signal is supplied to the digital signal processing circuit, and the digital signal recording device records the digital video signal on a recording medium after predetermined signal processing, and of signals to be supplied from the digital signal processing circuit to the digital signal recording device, a luminance signal is supplied in a state of an analog signal and a chrominance signal is supplied in a state of a digital signal.
According to another aspect of the present invention, the chrominance signal is supplied in a state of a digital signal sampled at the frequency of clocks of the image pickup element.
According to still another aspect of the present invention, an externally input luminance signal is supplied in a state of an analog signal, and an externally input chrominance signal is supplied in a state of a digital signal which is sampled at a frequency four times that of a subcarrier.
Therefore, when a signal from a solid-state image pickup element is A/D-converted and processed in a digital region, and the processed signal is then connected to an existing digital recording device, a luminance signal supplied from the solid-state image pickup element and an externally input luminance signal are supplied in an analog state, color-difference signals are supplied to the digital recording device in a state of digital color-difference signals at the sampling frequency of the solid-state image pickup * element, and an externally input chrominance signal is supplied after it is sampled at a frequency four times that of the subcarrier, and the sampled signal is converted into digital color-difference signals. Therefore, the arrangement of the circuit required for selecting one of a video signal input from the digital video camera and a video signal input from the external input terminal, and recording the selected signal on a recording medium can be simplified.
According to still another aspect of the present invention, when a signal from a solid-state image pickup element is A/D-converted and processed in a digital region, and the processed signal is then connected to an existing digital signal recording device, an externally input luminance signal to be supplied to the digital signal recording device is A/D-converted at the sampling frequency of the digital signal recording device, and an externally input chrominance signal to be supplied to the digital signal recording device is A/D-converted at, e.g., a frequency four times the subcarrier frequency.
According to still another aspect of the present invention, when a signal from a solid-state image pickup element is A/D-converted and processed in a digital region, and the processed signal is then connected to an existing digital signal recording/reproduction device, digital color-difference signals from a camera unit are supplied to a modulation circuit without changing their sampling frequency, e.g., four times the subcarrier frequency, and color-difference output signals from the digital signal recording/reproduction device are frequency-converted and are then modulated in the digital region.
According to still another aspect of the present invention, when a signal from a solid-state image pickup element is A/D-converted and processed in a digital region, and the processed signal is then connected to an existing digital signal recording/reproduction device, the sampling frequency of digital color-difference signals from a camera unit is converted, and color-difference signals to be output are modulated in an analog region.
In this manner, the number of components can be decreased, and an existing digital signal processing camera and an existing digital VTR can be easily connected.
An image pickup recording apparatus according to still another aspect of the present invention has an electronic zoom circuit for electronically enlarging or reducing an image. The apparatus has a first clock for operating an image pickup unit, and a second clock, having a frequency different from that of the first clock, for operating a recording unit. In the electronic zoom circuit, image pickup video signal data at the first clock rate is converted into video signal data at the second clock rate.
According to still another aspect of the present invention, a circuit for separating and forming a luminance signal and a chrominance signal from a digital signal obtained by A/D-converting a color image pickup element output signal is constituted by a plurality of stages of delay circuits, a plurality of coefficient multipliers for respectively multiplying the outputs from the plurality of stages of delay circuits with predetermined coefficients, an adding up circuit for adding up the outputs from the plurality of coefficient multipliers, and a chrominance signal forming circuit for forming a chrominance signal using some of signals output from the plurality of stages of delay circuits.
Therefore, since image pickup video signal data at the first clock rate for operating the image pickup unit and video signal data at the second clock rate for operating the recording unit are converted in the electronic zoom circuit, a video signal formed by a camera can be recorded by a digital recorder without being D/A converted, thus minimizing deterioration of image quality. In addition, since t;he number of digital circuit portions increases, high integration, low power consumption, and high precision can be realized.
The above and other objects and features of the present invention will become apparent from the following description of the specification and the drawings.